Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$246.81	11.400%	$274.9463	$274.95	$274.95	$274.90
Purchase #2	$92.54	8.521%	$100.4253	$100.43	$100.45	$100.40
Purchase #3	$238.69	12.476%	$268.469	$268.47	$268.45	$268.50
Purchase #4	$126.43	13.473%	$143.4639	$143.46	$143.45	$143.50
Purchase #5	$231.69	12.802%	$261.351	$261.35	$261.35	$261.40
Purchase #6	$131.77	4.250%	$137.3702	$137.37	$137.35	$137.40
Purchase #7	$57.65	8.177%	$62.364	$62.36	$62.35	$62.40
7 purchase totals =	$1,125.58		$1,248.3897	$1,248.39	$1,248.35	$1,248.50